Mortality Rates in Golden Shiners Fed High‐Fat Diets with or without a Dairy‐Yeast Prebiotic before Challenge with Flavobacterium columnare

Abstract

AbstractColumnaris, caused by Flavobacterium columnare, is a major bacterial disease of the golden shiner Notemigonus crysoleucas, especially when fish become stressed during handling and transport. Feed additives, such as a dairy‐yeast prebiotic, can decrease disease susceptibility in some fish species. Previous studies have indicated that diets with higher fat concentrations have improved the growth and survival of golden shiners. We conducted a study to determine whether a high‐fat diet alone or supplemented with a dairy‐yeast prebiotic could decrease mortality rates of golden shiners subjected to columnaris challenge. Golden shiners were assigned one of three diets with four replicate aquaria per diet and fed to apparent satiation twice daily for 16 weeks before the challenge. Diets (30.3 ± 0.31% crude protein; mean ± SE) were similar to a commercial formula and contained (1) 4% poultry fat (control), (2) 10% poultry fat, or (3) 10% poultry fat and 2% dairy‐yeast prebiotic. After the 16‐week feeding period, 15 golden shiners (2.2 ± 0.03 g) from each aquarium were stocked into different aquaria (experimental replicates were maintained) and exposed to 20 mL of columnaris bacteria in Sheih broth (optical density, 0.395 Å; at 560 nm; Sheih broth blank) for 18 h. Kidney cultures taken from moribund fish were streaked on Sheih agar to confirm the presence of columnaris and an active infection. Mortality in the 4% poultry fat (41.7 ± 12.9%) and 10% poultry fat (40.0 ± 6.1%) diets was high and not significantly different. Mortality for the dairy‐yeast prebiotic (6.7 ± 2.7%) diet was much lower and significantly different from that for the 4% and 10% poultry fat diets. Thus, the dairy‐yeast prebiotic effectively reduced mortality rates in golden shiners exposed to columnaris, but a high‐fat diet alone provided no protection relative to the lower‐lipid control diet.